1. Field of the Invention
The present invention is directed to a telecommunication system for transmitting video signals, including the audio component and other services such as telephone, data, facsimile, and even video signals of broadcast quality, over twisted pairs of telephone wires and using a personal computer system or TV/HDTV monitor.
2. Description of the Prior Art
For many years transmission of full motion video images was possible only over communication links especially adapted for broad band frequency transmission, as contrasted with the bandwidth of communication signals employed in the transmission of audio or data telephone communications. Such high-grade video communication links were considered to be necessary since a video signal deteriorates rapidly and unevenly across its frequency spectrum with increasing length of the communication link. A telephone communication infrastructure employing twisted pairs of wire for carrying communication signals has existed in this and virtually every other country of the world for many years. However, this conventional telephone infrastructure could not be used for the transmission of full motion video signals because of the degradation of those signals in passing over the twisted pairs of telephone lines.
A significant advance was achieved when a system was devised for compensating for the degradation of the video signal over a twisted pair of telephone wires by introducing an impedance of equal and vectorially opposite direction into the received signal. This signal treatment essentially reconstructs the signal to its original quality after transmitting it along a twisted pair of telephone wires. This new system allows full motion, color video to be transmitted for full duplex over conventional pairs of twisted telephone wires and is described in U.S. Pat. No. 5,283,637.
The feature of signal reconstruction or automatic compensation lends itself to use with existing telephone infrastructures. For example, a central office typically services an area from the central off hub to the most remote service location an average distance of 4.5 miles over twisted pairs of telephone wires. Typically, these twisted pairs do not extend over lengths greater than 6,000 feet before passing through manholes. Also, central offices are connected to each other by twisted pairs of telephone wires which likewise pass through manholes.
At each central office and manhole location interconnections exist in the existing telephone infrastructure that allow the automatic compensation circuitry of the invention to be inserted in both the subscriber line and in lines between central offices. By employing automatic compensation as described herein a bandwidth of 20 MHz can be maintained from the central office hub to the end user, which is at the subscriber location. This capability allows the broadband signal to be transmitted while meeting the demands of video conferencing, remote meter reading, and even the monitoring of hospitalized patients for vital signs using live video, as well as the transmission requirements of conventional telephone services.
According to the system of U.S. Pat. No. 5,283,637, the length of the twisted pair of telephone wires was determined and compensating resistors and capacitors were strapped into the circuit, on a permanent, or at least semipermanent basis, so as to provide an impedance proportional and in opposition to the known impedance of the twisted pair link. This impedance, impressed on a video signal, thereby negates effects of the known impedance on the broad band video signal from the video source. The resistors and capacitors which were strapped into the circuit were determined by the length of the twisted pair link. Different resistive-capacitive networks would be strapped into the system depending upon the length of the twisted pair, and compensation could be achieved for segments of unloaded twisted pairs of telephone wires up to six thousand feet in length or greater, depending upon the gauge of the wire employed, without amplification. When amplifiers are added to the end of a 6,000 foot segment, greater distances can be achieved.